It is previously known in this art to permanently anchor oral prostheses in the jaw bone by means of helical anchorage elements, so-called fixtures, of a biocompatible material, preferably pure titanium. That method which has proved to give the highest anchorage stability and which has been used clinically with considerable success for more than 20 years is the so-called osseo-integration method developed by Professor Per-Ingvar Br.ang.nemark et. al. and described in, for example,
Br.ang.nemark/Zarb/Albrektsson: "Tissue-Integrated Prostheses", Quintessence Books, 1985.
The method is based on a highly exact and atraumatic implantation technique of the fixture such that direct contact, i.e. an exact adaptation without interjacent bonding tissue, takes place between the fixture and the bone tissue proper. Such a direct contact between fixture and bone tissue creates the best preconditions for a really permanent anchorage of a dental prosthesis.
The helical fixtures which are of pure titanium are surgically implanted in the jaw bone in a first operation which is followed by an unloaded healing phase of critical length during which time the fixture is covered by intact mucous membrane. During this healing phase, the bone tissue grows onto and forms a unit with the implanted fixture. In a second operation, the fixture is then exposed and a spacer is applied to the fixture with the aid of a spacer screw. The dental prosthesis, in the form of a bridge construction, is then anchored in place by means of an anchorage screw which in its turn anchors in the spacer screw.
A bridge construction is anchored with the aid of a plurality of fixtures, for example six in number, and corresponding spacers which constitute connection members between the bridge construction and the fixtures. In order to be able to accomodate the extreme oral loadings to which the screw connection is exposed, the spacer is made of a biocompatible material of extremely good mechanical strength properties, for example titanium or the like.
To impart increased flexibility to the implant system, it is previously known in this art to employ angled spacers, see for example U.S. Pat. No. 3,732,621, DE 35 31 389 and implant systems of the ROTUBMENT type. The reason for wishing, in certain cases, to angle the spacers is that, using conventional systems, the anchorage screw for the dental bridge may on occasions be located in an unsuitable position. By means of an angled spacer, the anchorage screw can be placed in a more favorable position from the points of view of cosmetic appearance and dental technology.
A factor common to all of the prior-art angled spacers is that they are adjustable, which is a considerable disadvantage since it is difficult to reestablish the exact position if the original setting is loosened. This makes it difficult to get a dental bridge in position if the original setting has been disrupted. Moreover, such constructions are mechanically flimsy and suffer from poor strength because they are based on a combination of a ball with a narrow neck.
A further disadvantage inherent in these prior-art constructions is that pockets occur where bacteria may gather and give rise to inflammation.